This invention relates generally to systems and methods employing a charge coupled device (CCD) and particularly to such a system and method for measuring figures projected onto a CCD.
Charge coupled devices are finding use in a wide range of equipment requiring image sensing, such as verifying the acceptability of images or geometric figures. CCDs are used in conjunction with an optical lensing system which focuses the light from the object being investigated onto the CCD. Varying amounts of light on the individual pixels within the CCD array charge the pixels to different levels proportional to the incident light. The optical information from the object is, therefore, available in analog form across the pixels of the CCD array. The analog information is shifted out of the CCD and converted into digital form and stored in a digital memory where the various characteristics of the object can be investigated by the proper manipulation of the digital information. The individual pixels within a CCD array typically are closely spaced and are arranged horizontally in rows and vertically in columns so that a given CCD imaging device will provide a fixed number of pixels of information. As an example, the SID52501 CCD available from RCA Corporation has 320 vertical columns of pixels and 512 horizontal rows of pixels. Accordingly, the information is read out from the CCD and stored in 320 vertical columns and 512 horizontal rows. The pixels of a CCD are charged in proportion to the impinging energy. Accordingly, precise measurements of a geometric figure can be made by utilizing the differences in charge levels resulting from the partial illumination of some pixels. For example, a pixel which is only half illuminated because it is located near the edge of a figure receives half the charge of a fully illuminated pixel. Charge level variations of small percentages such as 5% are detectable so that precise measurements of figures projected onto a CCD can be made by utilizing the charge level variations. A CCD is also useful in imaging devices which generate figures by scanning because the CCD receives and stores the figure data without being scanned. Thus, the image which is generated by a scanning device, such as a kinescope, can be projected onto a CCD in a single frame without concern for the scanning rate of the kinescope. The data stored on the CCD can then be transferred to a digital storage device and processed by techniques needed to investigate scanned images. For these reasons, and because of the close spacing of the pixels, one ideal use for CCDs is that of measuring geometric figures by casting an image of the figure onto the CCD. The convergence of a color television kinescope can be measured by generating red, green and blue color bars on the kinescope and measuring the widths of the bars using a CCD.
The instant invention utilizes the advantages of a CCD by the provision of a CCD based figure measuring system and method wherein the charges received by each pixel within a pixel line of the CCD are summed and divided by a maximum charge per pixel value to provide a mean pixel signal which is multiplied by a dimension per pixel value to provide a dimension of the figure.